Piston and method of making same



Sept. 3, 1929. H. w. TROEGER PISTON AND METHOD OF MAKING SAME Filed Feb. 24, 1928 2 Sheets-Sheet 1 rll I r l 11 1 Sept, 3, 1929. H. w. TROEGER PISTON AND METHOD OF MAKING SAME Filed Feb. 24, 1928 2 Sheets-Sheet vlll attovmm d Patented Sept. 3, 1929.

oNiTEo STATES PATENT .orFlca.

PISTON AND METHOD OF MAKING- SAME.

Application fil ed February 24, 1928. Serial No. 256,725.

In the manufacture of pistons, particularly pistons for internal combustion engines, it is desirable that such pistons be constructed as light in weight as possible and that, for the sake of cheapness in manufacture, they be formed by a casting process. Cast iron pistons are heavy and pistons formed of a metal which is light in weight, such as an aluminum alloy, are not satisfactory due to uneven expansion of the metals- An" object of the present invention is to overcome these and other objectionable features of present day pistons by providin a composite piston which 5 may be formed y a casting process with pro-formed parts of a diiferent metal with I the parts firmly united in the casting operation', certain of such pro-formed parts providing a core part which becomes apart of the piston. A further object is to provide a cast metal piston with a pro-formed head of a difi'erent metal which is firmly united to the piston in the casting operation and to'provide a construction in which the pre-formed parts add greatly to the strength of the piston and obviate difliculties arising from the difference in expansion of the different metals.

A further object is to provide a construction wherein the piston may be cast in a mold with pre-formed parts set therein and the complete pistonreadily removed from the mold. A further object is to provide certain other new and useful features in the construction, arrangement and method of making the piston, all as hereinafter set forth and more. particularly pointed out in the appended claims, reference being had to the accompanying drawings in which- Figure 1 is a central vertical section through a complete mold and core illustrative of means for carrying out the present -,method of making pistons embodying the present invention;

Fig. 2 is an elevation of one-half of the mold taken at right angles to Figure 1 and showing the core in place therein and partly in elevation and partly in section; I

Fig. 3 is a'transversesection substantially upon the line 3 -3 of Figure 1;

Fig. 8 is a sectional detail showing the ends in use, due to the extreme heat application to their head ends and the comparatively cool condition of their skirt portions,

and it is necessary to provide for the dif ference in expansion between piston and oylinder walls. In casting such pistons difficulty arises in removing the core from the castpiston, it being necessary to destroy the core in order to remove it, and it has been found that greater efficiency is secured through providing a piston head formed of a metal similar to the metal of the cylinder wall.

In the present construction a head 1 is pre-formed of a suitable metal, preferably steel or iron which may be machined or otherwise formed into disk form with a shallow annular groove 2 inwardly from its periphery and with an undercut peripheral channel 3 having-holes 4 in the inwardly extending flange 5 formed by said channel, said channel being inclined in the direction of its Width, outwardly and toward the outer surface of the head or disk.

A casing or mold for casting therein of the piston, is formed in two like halves 6 with these halves detachably secured together by bolts 7 said halvesbeing formed .in their contacting faces with mating grooves together forming a channel 8 with branches opening into opposite sides of the mold and leading from an inlet opening 9 at the bottom of the mold to which inlet a pipe 10 is connected for conducting molten metal under pressure into the interior or diameter equal to the diameter of the chamber and fitting closely therein.

A core block 12 of cylindrical form and externally shaped and tapered to give the desired form to the interior surface of the piston skirt portion which is cast within the space between said core 'block and mold, 15 set within the chamber 1v of the mold, with an annnular shouldei 13 on said core closing the upper open end of the chamber and with a flange 14 thereon resting upon the upper end of the mold, the mold being notched as at 15 to provide vents at the upper end of the chamber for permitting air trapped therein to escape as the molten metal enters the mold through the branch passages 8.

In order that the skirt or cylindrical portion 16 of the piston may be cast with integral inwardly extending hollow bosses or bearings 17 and the core removed from the mold after casting, without destroying the core, the head end of said core is formed by a preformed sheet metal core member 18 which is set in the mold with .an end edge thereof engaged in the annular groove 2 of the head or disk 1 and the opposite end of said sheet metal core member is sleeved over a reduced end portion of the main core member with its inner end edge 19 extending to the plane of the axis of the bearing .mem-

. bers 17, which plane is the dividing or separating plane of the core parts so that in removing the core, the main core part 12 may be removed endwise from the cast piston and the sheet metal core member 18 remains in the cast piston and becomes an integral part thereof.

The main core member 12 is formed with an annular groove 20 to receive the end edge 19 9f the sheet metal core member 18,

a and is also formed with side recesses 21 and notches 22 opening thereinto, the recesses being designed to cast therein the lower halves of the bearing bosses 17 and the notches to form ribs 23 in the angle between said bosses and the wall of the piston skirt 16. The sheet metal core member 18 is formed with semi-cylindrical inwardly extending portions 24 corresponding in shape to the recesses 21 to confine the metal in the casting operation and cast therein, the upper half of the bearing bosses 17, notches 25 of the proper form and size being pro vided, within which the fillets 26 at the upper side of the bosses are cast. The semitubular portions 24' have the free side edges thereof turned inwardly forming flanges 27 which are embedded in the metal of the bosses 17 as the same are cast and thus firmly unite the sheet metal to the cast metal, said sheet metal forming the inner surface of the head end portion of the piston skirt and bosses down to the plane of the axis of the bosses which plane is the parting line he tween the core members 12 and 18. A rib 28 extends diametrically across the inner end of the core member 12 and fills the space between the adjacent inner ends of the boss forming parts 24 of the sheet metal core' member, andsylindrical cores 29 (Fig. 1) are supported at their outer ends by the walls 6 of the mold extending inwardly from said walls axially of the boss, forming recesses 21 and parts 24 with their inner ends abutting the rib 28, so that the bearing bosses ofthe piston will be cored out, forming bear.-

ings for the usual connecting rod pin.

Preferably, the main core member 12 is formed with a large axial bore extending in-- connected to the rib 28 by screws 3 1 passing loosely through openings in the bar and screwed into screwthreaded openings in said rib. The bar 33 is of a length to extend diametrically across the shell or core 18 with its ends resting upon a shoulder 35 formed by an annular offset in the shell. A small pipe 36 is inserted in a screwthreaded opening in the plug 31 and said plug is also provided with a vent opening 37.

With this arrangement of mold and core,

the skirt portion of the piston with its connecting-rod-pin bearings may be cast integral with a preformed piston head of a different material and the main part of the core removed therefrom without destroying the core, the sheet metal-portion of the core being firmly united to thecast skirt to form a part of the finished pistons. In this casting operation, molten metal under pressure, is forced into the mold through the passages 8, flowing into and filling the space 11 between the mold wall and core members 12 and 18. In filling this space, the metal flows into and fills the annular groove 3 in: the pre-formedi disk or head 1 which is laid in the bottom of the mold chamber, the metal also filli-ng the several small holes 4 in the flange 5 overlying said groove 3 and thus firmly locking the cast metal skirt portion of the piston to the head. If found desirable, a small annular groove 88 may be formed in the mold wall opposite the edge of the head 1 and i the head may be provided with small vent holes leadlng from the groove-3 in the head "move 3 may escape and said groove will be completely filled. with metal.

After the space between mold and core has been thus completely filled. the mold is removed by taking out the bolts 7 which. permit separation of the mold halves, and removal of the main core member 12 may be facilitated by admitting a small amount of water through the pipe 36 into the chamber 30 of the core, thus quickly contracting the core which may thus be lifted out of the cast piston skirt, but should it still adhere to the shell or core member 18, bylightly tapping upon the outer end of the rod 32, the shell and cast piston skirt will be released from the core member 12.

A piston is thus cast with a pro-formed head, which is firmly and permanently united to the cast skirt in the casting operation, and is so united thereto that the greater the expansion of the skirt relative to the head, the more firmly these parts will be held together, due to the annular channel 3 being extended and inclined outwardly and toward the outer face of the head, and the expansion of the skirt adjacent the head is limited tothat of the head due to this interlocking of the upper end of the skirt with the head.

The sheet metal core member 18 not only performs the function of a core part for givi'ng the desired interior configuration to the upper or head end of the skirt and the upper half of the bearing bosses so that the main or lower part 12 of the core may be removed endwise from the cast skirt without the necessity for destroying the core in order to get it out, but also becomes a permanent part of the finished piston, forming an interior shield for the upper end portion of the skirt to prevent oil from contacting and "thereby extracting the heat so rapidly that the lower end of he skirt will not be expanded to any material extent. The cast metal is a good conductor of heat and when the upper portion of the skirt is protected by the sheet metal lining member, the cast metal will conduct the heat rapidly to the lower end portion of the cast. skirt which will thus be heated sufficiently to expand equally with the upper end portion which is limited in expansion to the expansion of the head. Therefore unequal expansion between upper and lower ends of the skirt which usually causes the piston to crack adjacent its pin bearings, is overcome, the necessity for split ting the lower end portion is obviated, and said portion may have a wall of greater thickness and rigidity than is otherwise possible.

A permanent mold and core which may be used over and over again, may thus be employed and a piston is secured which is formed of dissimilar metals with the resultant advantages of lightness in weight, cheapness of manufacture, strength and rigidity and the obviating of difficulties arising from unequal expansion.

Obviously changes may be made within the scope of the appended claims in the form, construction and arrangement of parts, and in the instrumentalities employed in carrying out the method of manufacture, without departing from the spirit of the invention, and I do not therefore limit myself to the particular construction shown.

Havingthus fully described my invention, what ll claim is z-- 1. A composite piston including a preformed head having an annular groove, a pre-formed sheet metal member engaged at its end edge Within said groove and formed t conform to the desired interior configuration of a skirt portion of the piston, and a cast metal skirt portion outside of and conforming to the exterior of said sheet metal member. v

2. A piston as characterized in claim 1, said pre-formed head being formed to receive portions of the cast metal skirt portion to unite said head and skirt portion, said cast metal skirt portion conforming to the exterior of said sheet metal member to hold said member in place.

3. The method for manufacturin pistons having cast metal skirt portions w ich consists in providing a sheet metal interior member formed to conform to the interior configuration of a portion of the piston skirt and forming a core part therefor, providing an exterior mold, setting said sheet metal member within the mold, and then casting the skirt portion of the piston Within the mold between said member and mold wall.

4. The method for producin pistons having a cast metal skirt provide with interior bearing bosses which consists in roviding an exterior mold, providing a, preormed sheet metal core member shaped to conform to the desired interior configuration of the skirt portion of the piston and the upper half of said bearing bosses, placing said core member within the mold, providing a removable core member having an exterior configuration to conform to the desired interior shape o-fthe lower end portion of the skirt and lower half of said bearing bosses thereon, and then casting said skirt and bearing bosses within said mold between it and said core members.

5. The method of producing a composite piston having a pre-formed head, a cast metal skirt provided with interior bearing bosses,

and a preformed lining for said skirt adja-' within the mold in engagement with said gaged with. said lining member, and then head and spaced from the mold wall, procasting the skirt and bosses within said mold vidmg a core member shaped to form the between the wall thereof and said core and 10 desired interior configuration of the lower lining member and integral with said head.

5 end portion of the skirt and the lovvfer half In testimony whereof I affix my signature.

of said bearing passes, placing said core member in said mold With its inner end en- HERMAN XVALTER TROEGER. 

